Anaerobic reactor for the removal of long chain fatty acids from fat containing wastewater

ABSTRACT

The invention presented is an apparatus specifically designed for the high rate anaerobic treatment of (waste)waters with relatively high concentrations of lipidic compounds, referred to as the Inverted Anaerobic Sludge Blanket (IASB) reactor. Contrary to conventional anaerobic reactors, it avoids the need of sludge with good settling properties and exploits the problem of sludge flotation due to long chain fatty acid (LCFA) or biogas adsorption onto the sludge and/or biogas encapsulation by the sludge. Furthermore, it provides an increased specific sludge surface area for better LCFA degradation. It is fed from the top and is equipped with a separation step at the bottom. Reactor contents are thoroughly mixed by the novel combined action of a gas lift loop and a liquid recycle over the reactor. The reactor can be operated in continuous and sequential mode. Although it is specifically designed for lipid degradation, its application is not limited to this.

FIELD OF THE INVENTION

The invention presented is an apparatus specifically designed for thehigh rate anaerobic treatment of (waste)waters with relatively highconcentrations of lipidic compounds, referred to as the InvertedAnaerobic Sludge Blanket (IASB) reactor and a method to treat this kindof waters.

STATE OF THE ART

More and more people are becoming aware of the need for a sustainablesociety. Using renewable products and controlling pollution are ways toachieve sustainability. Both are combined when wastewater isbiologically treated in the absence of oxygen: through the action ofanaerobic bacteria organic pollutants present in wastewater areeffectively converted into biogas, a gas that mainly consist of methane(CH₄) and carbon dioxide (CO₂) and is a renewable energy source. Thisgas can then be used to produce e.g. useful electric energy. Worldwideanaerobic technology is being successfully applied to treat effluentsfrom e.g. breweries and the paper industry using compact wastewatertreatment installations. An example of a widely spread applied anaerobictechnology is the upflow anaerobic sludge blanket (UASB).

A major group of organic pollutants which has shown very difficult to beconverted into biogas are the lipids. Because of this, they are usuallyremoved from wastewater using technologies that require energy insteadof producing energy. In this way, these technologies do not contributeto a sustainable society. The current invention, referred to as theInverted Anaerobic Sludge Blanket, makes it possible to efficientlyremove lipids from wastewater and convert them into useful bioenergy inthe form of biogas.

The application of the invention opens up new markets for theapplication of anaerobic technology. Previously, industries at whichwastewaters are produced with relatively high lipid content werepractically off-limits. These industries include edible oil and fatrefineries, olive oil mills, dairy industries, wool scouring, meat,poultry and fish processing industry.

High rate anaerobic treatment of wastewater is possible by separatingthe solids retention time (SRT) from the hydraulic retention time (HRT).To achieve this, different separation methods are available. It is onthis principle that virtually all patented technologies concerninganaerobic treatment of wastewater are based. The difference between thetechnologies is the separation method applied to keep biomass inside thereactor. Between these technologies, the anaerobic membrane bioreactor(AMBR) may be considered as different, since separation is essentiallybased on size and not on sedimentation. Although the AMBR has been shownto be useful for e.g. continuous anaerobic sulphate reduction usingextremophiles and may be used for removal of dissolved organicpollutants, they are less suitable for lipids containing wastewater dueto increased membrane clogging. With the current state-of-the-artmembrane technology intensive and therefore expensive cleaning regimeswould be required.

Tilted plate separators (TPS) may be applied to continuously separatebiomass and solids or oil from wastewater (NL patent 7208503, U.S. Pat.Nos. 4,202,778 & 4,477,344). They have been applied on a full-scalelevel for separating e.g. biologically produced elemental sulphur fromwastewater. It is less common for them to be integrated in continuousanaerobic reactors (U.S. Pat. No. 5,904,850), especially when relativelybig amounts of gas are produced or circulated. This is due to thedisturbing effect of gas on the settling of solids in between theparallel tilted plates. Thus, enough degassing surface would need to beprovided next to the integrated TPS to prevent disturbance of the solidssettling process. This can be done by increasing the reactor surface atthe top. This, however, considerably increases the costs of reactorconstruction compared to a simple cylindrical reactor. Another way wouldbe simply using bigger reactors. Considering the fact that integratingthe TPS in the reactor is, amongst others, contemplated as to reducespace requirements, this option may seem a bit forceful and therefore adisinvestment.

When lipids containing wastewater is anaerobically treated using highrate reactors not only considerable amounts of biogas would be produced:Due to long-chain fatty acid (LCFA) adsorption sludge flotation occurs.Top-mounted TPS are not suited to retain floating sludge within areactor.

Three-phase separation is the most common way to maintain high solidsconcentrations within continuous high-rate biogas producing reactors.The most used three-phase separators are of the gas cap variety (e.g.European patents 0808805 & 1291326, U.S. Pat. No. 5,855,785). The gascaps are essentially inverted funnels in which biogas is accumulated.Wastewater continues upwards, while sludge settles back into the sludgeblanket maintained in the bottom part of the reactor. The sludgeblankets usually consist of granular sludge, although flocculate biomassmay be applied as well. The best known high rate reactor using thistechnology is the upflow anaerobic sludge blanket (UASB) reactor. Thesereactors have up to three layers of three-phase separators in the top.Mixing is achieved through biogas production and application of anupflow velocity of typically 1 m/h.

Reactors capable of dealing with higher organic loading rates arebecoming more and more common, however, and substituting the UASBreactor. Most of them still apply the same three-phase separators,however. The difference is that they are more compartmentalised. Thisway a lower highly turbulent zone and an upper clarification andsettling zone can be created. These compartments are separated from eachother by layers of three-phase separators (European patents 1408009 &0808805, U.S. Pat. No. 4,609,460). Through this compartmentalisationmore intensive mixing can be obtained by applying higher upflowvelocities and recycling biogas using gas lift loops (U.S. Pat. Nos.5,338,447 & 4,609,460, EP 1408009). Yet another way of maintainingbiomass in a high-rate anaerobic reactor and intensifying the process isthrough immobilisation onto a carrier material, e.g. pumice. Thus, afluidised bed is obtained. Again, intensive mixing may be achieved usinga gas lift loop (U.S. Pat. No. 4,482,458) or a liquid recycle.

Separation using three-phase separators is based on sedimentation ofsolids: Due to their higher density solids have the tendency to settleto the lower parts of the reactor. Floatation of sludge may sporadicallyoccur due to encapsulation or adsorption of biogas. Most of the newerhigh-rate reactors are equipped to deal with limited amounts of floatingsludge. Usually gas lift loops are involved. These are used to suckfloating sludge from above the three-phase separators back into thereactor (U.S. Pat. Nos. 4,609,460 & 5,338,447) or to swing particlesfrom under the three-phase separator back into the reactor (U.S. Pat.No. 5,855,785). Another way is to simply provide for a separate sectionwhere particles entrained with the gas loop have a chance to settle backinto the reactor compartment (EP 1408 009, U.S. Pat. No. 4,482,458).Excessive amounts of floating sludge such as occur during LCFAdegradation form a severe problem for high-rate anaerobic reactorsequipped with three-phase separators. They are not able to maintainsludge inside the reactor and consequently bioactivity is lost leadingto eventual process failure.

Continuous processes have been patented in which not a specificseparator is applied. Enough space is provided to allow forsolid-liquid-gas separation. U.S. Pat. No. 6,048,459 and 2003085171disclose processes where external gas is provided to create gas liftsfor increased mixing at low shear stress. The gas lifts drag solidsalong and lead to quiescent zones where they may settle. Subsequently,the solids are sucked back into the reactor through the gas loop downer.Gas is collected in the head space of the reactor. It may be appreciatedthat due to the absence of separation equipment it is difficult toretain floating sludge within such reactors.

Another way to prevent specific separation equipment is throughimmobilisation of biomass onto fixed surfaces. Enough surface area hasto be provided, however, as to prevent mass transport limitation. Onesuch way is described in Spanish patent 2212895. Here tubes are usedonto which biomass is fixed. Mixing is obtained using gas lift loops.Although biomass floatation and subsequent washout is obviouslyprevented if LCFA containing wastewater is treated, other problems areencountered when fixing biomass onto surfaces: the limited surface areaonto which LCFA may adsorb. This unavoidably leads to mass transportlimitation. Furthermore, the ability of biomass to attach to surfaces isseverely affected by the presence of LCFA resulting in eventualdetachment and washout.

As previously mentioned, biomass can also be immobilised onto particles(biocarriers) thus forming a fluidised bed. Here, two options areavailable: The biocarrier applied can either have a higher density (U.S.Pat. No. 4,482,458) or a lower density than water (U.S. Pat. No.4,454,038 & 2002/0185437). When particles with a higher density thanwater are applied a fluidised bed in the bottom section of the reactoris formed. Floatation due to LCFA adsorption would definitely lead tosludge washout and activity loss. When particles with a lower densitythan water are applied an inverted floating fluidised bed is obtained.These fluidised beds are fed from the top and provided with a means forfluidisation. This can be a liquid recycle from the reactor bottom tothe reactor top (U.S. Pat. No. 4,454,038). Fluidisation can also beobtained by applying a gas lift loop (U.S. patent 2002/0185437 and U.S.Pat. No. 4,454,038). In this case gas either containing oxygen orhydrogen is provided using a compressor. Furthermore, gas may berecycled using a further compressor or pump. Fluidised beds make use ofbio-attachment to particles. As previously stated, the ability ofbiomass to attach to surfaces is severely affected by the presence ofLCFA. Thus, the floating particle bed would only take up space insteadof serving a definite purpose, thus reducing reactor efficiency.Preferably, biocarriers are avoided. A big part of the energy that wouldbe generated in the form of biogas is lost to energy intensive gascompression for gas provision purposes. Gas compression is best avoided.

Instead of a continuous process a fed-batch process may be applied forLCFA removal from wastewater. The anaerobic sequencing batch reactor(ASBR, U.S. Pat. No. 5,185,079) is such a process. It may be fed withLCFA containing wastewater after which LCFA adsorbs onto the biomasspresent. After feeding LCFA is allowed to be broken down and the biomassis allowed to settle. The then treated water is drawn off. The ASBRprevents the problems related to LCFA adsorption encountered withcontinuous processes. Nevertheless, the principles of solids separationare still based on sedimentation. If mixing is applied using a fluidrecycle, the recycle is applied from below as to fluidise the sludgeblanket. Furthermore, the ASBR as described in U.S. Pat. No. 5,185,079is limited to sequential operation. If operated in continuous mode thesame problems with floating sludge would be encountered.

SUMMARY OF THE INVENTION

The current invention is a reaction vessel providing the means forhigh-rate anaerobic LCFA degradation. The reaction vessel is designed insuch a way that sludge buoyancy due to LCFA adsorption and/or biogasencapsulation or adsorption are advantageously used to maintain sludgeinside the reaction vessel. Contrary to conventional anaerobictechniques, neither sludge granulation nor biocarriers are used tomaintain biological activity inside the reactor. In fact, it is anobjective of the current invention to demote sludge granulation toincrease the adsorption surface for LCFA and sludge buoyancy due tobiogas encapsulation. A further objective is the inducement of a naturalgas lift effect due to biogas production without the application of acompressor or pump. Yet another objective is increasing LCFA degradationefficiency by applying a liquid and sludge recycle over the reactor frombottom to top. This recycle is joined, and thus intensely contacted,with LCFA and/or other organic constituents containing influent andinjected into one or more draft tubes in a downward motion, thuscreating a downflow inside the draft tube(s). Due to this downflowsuction is created leading to entrainment of floating sludge leading tofurther intense contact between sludge and reactor influent and furtherliberating encapsulated biogas. A still further objective is to providean effluent virtually free of suspended solids by applying a separationstep at the bottom of the reactor.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a schematic representation of a possible configuration ofthe current invention.

FIG. 2 shows a possible configuration of the inclined plate settler atthe bottom.

FIG. 3 shows possible draft tube configurations.

DETAILED DESCRIPTION OF THE INVENTION Method

A preferred embodiment of a process according to the present inventionprovides a process for the biological anaerobic treatment of wastewaterby converting constituents into gaseous compounds, said processcomprising:

-   -   a)Intense mixing of influent with reactor liquor extracted from        the bottom section of the reaction vessel without damaging        bacteria present;    -   b)Intense contacting of wastewater with the reactor sludge;    -   c)Demoting of sludge granulation to increase the contact area        between bacteria and constituents to be converted into gaseous        compounds without damaging the bacteria;    -   d)Dispersing floating sludge into the reactor without damaging        the biocatalysts by injecting liquid into at least one downer;    -   e)Liberating encapsulated gaseous compounds by applying low        shear stress;    -   f)Mixing of reactor contents through a natural gas lift effect        induced by the production of gaseous compounds;

g)Removing gaseous compounds at the top of the reactor;

h)Separating solids from purified water using a separation step thusretaining sludge inside the reactor vessel and maintaining activity;

-   -   i)Removing purified water from the reaction vessel after said        separation step;    -   j)Removing sludge as required from the vessel;    -   k)Preventing excessive foaming by spraying treated water onto        the floating sludge layer;    -   l)Provision of influent either in a continuous mode or in a fed        batch mode.

In an embodiment of the present invention the constituents to be removedfrom the water are lipidic compounds (long chain fatty acids (LCFA)),which induce sludge floatation after being adsorbed onto the sludge. Inanother embodiment of the present invention the constituents to beremoved are organic compounds such as volatile fatty acids, ethanol andaromatic compounds. The gaseous compounds produced are mainly methanegas (CH₄) and carbon dioxide (CO₂) to form biogas.

In a further embodiment of the current invention adsorption is promotedby joining a sludge recycle extracted at one or more outlets at thebottom of the reactor with reactor influent, after which the mixture isdownwardly injected into at least one downer. The downward injection ofthis flow creates suction at the top of the downer thus entrainingfloating sludge from the top of the reactor into the downer. This wayfurther constituent adsorption is obtained. The flow in the downer ishighly turbulent and will initially stimulate the liberation of biogaspossibly encapsulated by the sludge. Nevertheless, the sludge will bedragged downward by the liquid flow.

In a yet further embodiment of the current invention after constituentadsorption, biogas is mainly produced in the compartment outside thedowner: the riser section. This leads to a natural gas lift effect thusstimulating liquid circulation in the reactor. Due to biogas productionand organic constituent adsorption, foaming will be induced. In anembodiment of the current invention this is counteracted by sprayingtreated effluent in the top of the reactor.

In a still further embodiment of the current invention the liquid levelinside the reaction vessel is maintained using a vertically extendedtube equipped with a siphon breaker to the required liquid level andconnected to the purified water outlet(s) of the reaction vessel.

In a still further embodiment of the current invention the microbialpopulation inside the reactor consists of anaerobic hydrolysingbacteria, acidifying bacteria, acetogenic bacteria and methanogenicbacteria. In a further embodiment the microbial population alsocomprises bacteria specialised in hydrolysing lipids and anaerobicallyoxidising long chain fatty acids.

Apparatus

A preferred embodiment of an apparatus according to the presentinvention is a vertically elongated reaction vessel for the biologicalanaerobic treatment of wastewater comprising a wastewater inlet systemfor reactor liquor and influent mixing and subsequent downward injectionthrough one or more inlets or nozzles into one or more draft tubeslocated under the water level and mounted of the bottom of the reactionvessel, a reactor liquor recycling system comprising one or more outletsor nozzles for the suction of reactor liquor located in the bottomsection of the reactor vessel, a means for recycling reactor liquor fromthe bottom section to the wastewater inlet system, a means forseparating solids from purified water situated in the bottom section ofthe reaction vessel, a treated wastewater outlet system comprising oneor more outlets or nozzles located after the said means for separatingsolids for the removal of treated water out of the reaction vessel, oneor more spraying nozzles situated in the top of the reactor for sprayingtreated water onto the floating sludge as to counteract foaming, and abiogas collection system located in the top of the reactor above thespraying nozzles comprising one or more outlets. The apparatus ishereafter referred to as the Inverted Anaerobic Sludge Blanket (IASB)reactor.

In an embodiment of the present invention the IASB reactor has acylindrical shape with a height to diameter ratio of at least 2,equipped with one or more cylindrical draft tubes open at both ends thatserve as downers, comprising a separator consisting of two or moreconcentric funnel shaped surfaces with the inclined surfaces each makingan equal angle with the horizontal and of which the top one is linedwith the reactor wall and the bottom one is connected to the reactorbottom. The draft tubes are essentially submerged and fixed above thefunnel shaped separator at such a distance to provide for a quiescentzone for non-buoyant solids to settle to the bottom from where they maybe recycled to the top of the reactor or, if necessary, discharged. Thedraft tubes should be sized in such a way that sludge entrainment fromthe top and intensive mixing due high liquid flow rate are assured andappreciable biogas production in the draft tubes is prevented. Thus, theliquid residence time in the draft tubes should be limited. The totalcross sectional area of the downer section is essentially smaller thanthe cross sectional area of the riser section. It is further possible toapply different cross sectional areas at different heights of the drafttube(s) as to stimulate sludge entrainment and create a more turbulentzone in the top (smaller cross section) and a less turbulent zone in thebottom (bigger cross section) of the draft tubes. Yet anotherpossibility is the application of a restriction in the top section ofthe draft tubes. The inclined surfaces of the funnel shaped separatorshould have such an inclination that close to laminar flow is assuredfor optimum solids settling. The angle between the inclined surface andthe horizontal preferably is between 50 and 75°. The treated wastewateroutlet system is situated in the compartment between the cylindricalbottom section of the reactor and the outside of the lowest funnelshaped surface of the separator. The effluent system should compriseenough outlets as to prevent short circuiting over the separator andthus biomass entrainment due to preferential flows.

In another embodiment the reactor has a cylindrical shape and isequipped with a submerged wall to create two compartments, i.e. thedowner and riser compartment. It is further possible to apply two wallsto create different cross sectional areas at different reactor heightsas to improve sludge entrainment and constituent adsorption. The reactoris further equipped with two or more inclined parallel plates serving asseparator. The inclined plates are joined with the walls. Some space isallowed for between the separator and the submerged wall as to preventturbulent conditions near the separator influent area. The angle betweenthe horizontal and the inclined plates preferably is between 50 and 75°.The treated wastewater outlet system is situated in the compartmentbetween the cylindrical bottom section of the reactor and the inclinedplate separator. The effluent system should comprise enough outlets asto prevent short circuiting over the separator and thus biomassentrainment due to preferential flows.

In yet another embodiment of the present invention the reactor has arectangular or other symmetrical shape other than cylindrical with thevertical length being bigger than the horizontal one, comprising one ormore separator units consisting of two or more inclined parallel plates.The one or more downers may be created by applying submerged cylindricaltubes located above the separator units or by dividing the reactor intosections using submerged walls located above the separator units. Thevertical spacing between riser/downer section and separation sectionshould be such that turbulent conditions near the separator influent areprevented. It is crucial that the compartment(s) with downward flow havea smaller cross sectional area than the riser compartment(s).

The invention is in no way limited to the above described embodiments.In fact many variations on the above described embodiments are possiblewithin the scope of the claims.

DETAILED DESCRIPTION OF THE FIGURES

A possible configuration of the present invention is shown in FIG. 1. Itconcerns a reactor 1 suited for sequential and continuous treatment ofe.g. LCFA containing wastewater. In contrast with conventional anaerobictechnology, the sludge blanket is essentially a floating blanket. It istherefore beneficial to feed the reactor from the top (2) and draw offeffluent at the bottom (3). It cannot be completely prevented that somesludge settles at the bottom of the reactor. To prevent sludge washout,a separation step 4 is located at the bottom of the reactor beforeeffluent exit points. One lamella separator consisting of two parallelplates is located at the bottom to keep the sludge inside the reactor.It is placed in such a way that gas cannot enter them and disturb theseparation process. The inclined parallel plates are placed at an angleof 70° with the reactor bottom. Mixing is achieved in two ways. Firstly,reactor influent 2 is mixed with a reactor liquor recycle 5 and theninjected downwards into one or more reactor downers 6. In FIG. 1 onedowner is shown created using a submerged wall. The liquid recycle isdrawn from the bottom of the reactor using a pump 7. It also serves topump settled sludge from the bottom to the top. Furthermore, sludgesettled at the bottom will be exposed to shear forces, thus increasingthe sludge surface area. Pump 7 can also be used for periodic sludgedischarges to prevent excessive solids build-up. Further mixing isprovided by an internal gas lift loop due to biogas production in riser8. Thus, liquid with sludge laden with LCFA circulates to the top of thereactor and closes the gas lift loop. This is indicates with curvedarrows in FIG. 1. The downer area is essentially smaller than the riserarea. This is to increase turbulence in the downer and biogas release inthe riser. Biogas 9 leaves the reactor at the top. To counteract foamingdue to biogas production and the presence of LCFA, the reactor may beequipped with water sprays in the top of the reactor. The water used forthe sprays is the treated reactor effluent.

FIG. 2 shows a schematical representation of an inclined plate settler 4consisting of two concentric funnels. It shows the side view (FIG. 2 a)and the top view (FIG. 2 b) of the bottom section of a reaction vessel1. In the top view a possible configuration of outlets 10 is alsoschematically shown.

FIG. 3 shows three different draft tube configurations. FIG. 3 a showsone draft tube concentric with reactor vessel 1. The arrow demonstratesthe liquid flow through downer 6. The space between the downer 6 andvessel wall is the riser area 8. FIG. 3 b shows a draft tube with arestriction as to increase sludge entrainment and local turbulence andadsorption. FIG. 3 c shows two concentric draft tubes. Advantages of theconfigurations shown in FIGS. 3 b and 3 c are increased entrainment andinitial turbulence and the possibility for liberated encapsulated biogasto freely rise to the top of the reactor without disturbing the downwardliquid flow.

1. An apparatus for biological anaerobic treatment of wastewater,comprising a vertically elongated reaction vessel (1), a wastewaterinlet system for reactor liquor (5) and influent (2) mixing andsubsequent downward injection through one or more inlets or nozzles intoone or more draft tubes located under the water level and mounted offthe bottom of said reaction vessel (1), a reactor liquor recyclingsystem comprising one or more outlets or nozzles for the suction of saidreactor liquor (5) located in the bottom section of said reactor vessel(1), a means (7) for recycling said reactor liquor (5) from the bottomsection to said wastewater inlet system, a means (4) for separatingsolids from purified water (3) situated in said bottom section of saidreaction vessel, a treated wastewater outlet system comprising one ormore outlets or nozzles (10) located after the said means (4) forseparating solids for the removal of treated water (3) out of saidreaction vessel (1), one or more spraying nozzles situated in the top ofthe reactor for spraying said treated water (3) onto the floating sludgeas to counteract foaming, and a biogas collection system located in thetop of the reactor (1) above the spraying nozzles comprising one or moreoutlets.
 2. The apparatus of claim 1, wherein said reaction vessel (1)has a cylindrical shape with a height to diameter ratio of at least 2,equipped with one or more cylindrical draft tubes open at both ends thatserve as downers (6), comprising a separator (4) consisting of two ormore concentric funnel shaped surfaces with the inclined surfaces eachmaking an equal angle with the horizontal and of which the top one islined with the reactor wall and the bottom one is connected to thereactor bottom.
 3. The apparatus of claim 2, wherein said draft tubesare essentially submerged and fixed above the funnel shaped separator(4) at such a distance to provide for a quiescent zone for non-buoyantsolids to settle to the bottom from where they may be recycled to thetop of the reactor (1) or, if necessary, discharged.
 4. The apparatus ofclaim 2, wherein said draft tubes should be sized in such a way thatsludge entrainment from the top and intensive mixing due high liquidflow rate are assured and appreciable biogas production in the drafttubes is prevented.
 5. The apparatus of claim 2, wherein the total crosssectional area of the downer section (6) is essentially smaller than thecross sectional area of the riser section (8).
 6. The apparatus of claim2, wherein the one or more draft tubes have different cross sectionalareas at different heights to stimulate sludge entrainment and create amore turbulent zone in the top and a less turbulent zone in the bottomof the draft tubes.
 7. The apparatus of claim 2, wherein a restrictionis applied in the top section of the said one or more draft tubes. 8.The apparatus of claim 2, wherein the angle between the said funnelshaped surfaces and the horizontal is between 50 and 75° C.
 9. Theapparatus of claim 1, wherein said reaction vessel (1) has a cylindricalshape, with a height to diameter ratio of at least 2, is equipped with asubmerged wall to create a downer (6) and a riser (8) compartment ofwhich the downer area is essentially smaller than the riser area (8) andis further equipped with a separator (4) consisting of two or moreinclined parallel plates which are joined with the walls and make anangle between 50 and 75° C. with the horizontal.
 10. The apparatus ofclaim 9, wherein said wall is essentially fixed above said separator atsuch a distance to provide for a quiescent zone for non-buoyant solidsto settle to the bottom from where they may be recycled to the top ofthe reactor or, if necessary, discharged.
 11. The apparatus of claim 9,wherein a second wall is applied to create different cross sectionalareas at different reactor heights as to improve sludge entrainment andconstituent adsorption.
 12. The apparatus of claim 1, wherein saidreaction vessel (1) has a rectangular or other symmetrical shape otherthan cylindrical with the vertical length being bigger than thehorizontal length, comprising one or more separator units (4) consistingof two or more inclined parallel plates.
 13. The apparatus of claim 12,wherein said reaction vessel (1) has one or more downers (6) created byapplying submerged cylindrical tubes located above the separator unitsor by dividing the reactor (1) into sections using submerged wallslocated above the separator units and providing for enough spacingbetween said cylindrical tubes or said wall to provide for a quiescentzone for non-buoyant solids to settle to the bottom from where they maybe recycled to the top of the reactor (1) or, if necessary, discharged.14. The apparatus of claim 13, wherein said one or more downers (6)essentially have a smaller cross sectional area than the one or morerisers (8).
 15. A method for the biological anaerobic treatment ofwastewater by converting constituents into gaseous compounds, saidprocess comprising: a) Intense mixing of influent (2) with reactorliquor (5) extracted from the bottom section of the said reaction vessel(1) without damaging bacteria present; b) Intense contacting ofwastewater with reactor sludge; c) Demoting of sludge granulation toincrease the contact area between bacteria and constituents to beconverted into gaseous compounds without damaging the bacteria; d)Dispersing floating sludge into the reactor (1) without damaging thebio-catalysts by injecting said mixture of reactor liquid and influentinto at least one downer (6); e) Liberating encapsulated gaseouscompounds by applying low shear stress; f) Mixing of reactor contentsthrough a natural gas lift effect induced by the production of gaseouscompounds; g) Removing gaseous compounds (9) at the top of the reactor(1); h) Separating solids from purified water using a separation step(4) thus retaining sludge inside the reactor vessel (1) and maintainingactivity; i) Removing purified water (3) from the reaction vessel (1)after said separation step (4); j) Removing sludge as required from thevessel (1); k) Preventing excessive foaming by spraying treated water(3) onto the floating sludge layer; l) Provision of influent (3) eitherin a continuous mode or in a fed batch mode.
 16. The method of claim 15,wherein the constituents to be removed from the water are lipidiccompounds (long chain fatty acids (LCFA)).
 17. The method of claim 15,wherein the constituents to be removed are organic compounds such asvolatile fatty acids, ethanol and aromatic compounds.
 18. The method ofclaim 15, wherein said gaseous compounds produced are mainly methane gas(CH₄) and carbon dioxide (CO₂) to form biogas (9).
 19. The method ofclaim 15, wherein said biogas (9) is liberated from sludge in the atleast one downer (6) due to turbulence.
 20. The method of claim 15,wherein biogas is mainly produced in the riser section (8) of thereaction vessel (1) thus inducing the said natural gas lift effect. 21.The method of claim 15, wherein the liquid level inside the reactionvessel (1) is maintained using a vertically extended tube equipped witha siphon breaker to the required liquid level and connected to thepurified water outlet(s) of the reaction vessel (1).
 22. The method ofclaim 15, wherein the microbial population inside the reactor (1)consists of anaerobic hydrolysing bacteria, acidifying bacteria,acetogenic bacteria and methanogenic bacteria.
 23. The method of claim15, wherein the microbial population also comprises bacteria specialisedin hydrolysing lipids and anaerobically oxidising long chain fattyacids.